class Solution {
    const int INF = -0x3f3f3f3f;
public:
    int maxProfit(vector<int>& prices) {
        int n = prices.size();
        vector<vector<int>> f(n, vector<int>(3, INF)), g(n, vector<int>(3, INF));
        f[0][0] = -prices[0], g[0][0] = 0;
        for (int i = 1; i < n; i++)
        {
            for (int j = 0; j <= 2; j++)
            {
                f[i][j] = max(f[i - 1][j], g[i - 1][j] - prices[i]);
                g[i][j] = g[i - 1][j];
                if (j - 1 >= 0) g[i][j] = max(g[i - 1][j], f[i - 1][j - 1] + prices[i]);
            }
        }
        int ret = 0;
        for (int k = 0; k <= 2; k++)
            ret = max(ret, g[n - 1][k]);
        return ret;
    }
};